The invention relates to an implant for an improved endoprosthesis, of the type shown in German Pat. No. P 24,54,181.9. The implant is compatible with the skeleton and also forms a strong connection between the prosthesis and the bone immediately after the implantation without the use of bone cement.
An artificial bone joint replacement comprised of sintered oxide ceramic material is proposed in German Auslegeschrift No. 2,318,459. This publication describes a bone joint head on a worked femur head or a joint roller which is in engagement with the artificial joint socket. The socket also is comprised of sintered high-melting point metallic oxides. This type of artificial joint has a number of difficulties in use. The femur bone head can be worked only poorly into a prismatic polygon. The great variations among femur heads does not permit too close a fit of the implant on every femur head. Moreover, there is a danger of bone fracture in the region of the neck of the femur as a result of unpredictable loading, since considerable torques occur when the implant is screwed into the bone with a self-tapping thread.
A report by F. Betzel: "Kunststoffe in der plastischen Chirurgie der Gelenke" (Plastics in plastic surgery of the joints), which appeared in "Melsunger Medizinischpharmazeutische Mitteilungen", Issue 100 (1963), pages 2478-86, notes that endoprostheses were introduced by the Judet brothers and had their first clinical applications in 1948. Endoprostheses were then made of metal and plastic. Plastic hip surgery with Pyrex-Bakelite caps by Smith-Peterson occured. Because of pain caused the wearer of the prostheses by loading or stress and by his movement, because of the occurence of infections, because of prosthesis material damage and, in some cases, also on account of a degenerative shrinkage of the head and neck stump of the bone, such plastic prosthesis caps often have had to be removed soon after implantation. Such a cap often cannot long remain on the bone stump because the cap fits on loosely.
According to German Utility Model No. 75 09 026, elimination of the above described disadvantages has been attempted by uniting the loosely mounted prosthesis cap closely to the joint head, using as little bone cement as possible. Such a cap is made from metal and it is uneven on its inside surface to engage the bone and the cement. The cap has an opening leading to the outside for insertion of the cement.
Other cap shaped composite endoprostheses of metal and plastic are known from Swiss Pat. No. 560,538 and from German Pat. No. 876,739. The artificial joint head is spherically or mushroom shaped and the anchoring stem or shank mounted on the underside of the prosthesis may simply be straight or curved.
Although these implants permit careful treatment of the bone and also do not aggravate bleeding conditions during the implantation, they have not proven successful in practice because the metal and plastics materials employed do not promote long life for the implanted endoprosthesis. Moreover, with ceramic implants, experience has shown that the design possibilities have not yet been fully exhausted. In particular, in the use of these artificial joint replacement parts, various disadvantages, which can be traced back to the design of the hip joint prosthesis, have been manifest.